The segment polarity genes act via cell-cell interaction to establish and maintain pattern within the segmental primordia of the Drosophila blastoderm. Genetic and molecular data indicate that one of these, wingless (Drosophila int-1), encodes a secreted protein which acts as an intrasegmental signal. Through extensive searches for late zygotic lethal mutations with specific maternal effects, our laboratory has identified two genes, porcupine and dishevelled, which produce embryonic and imaginal phenotypes similar to those of wingless. Both genes are required for the known regulatory effects of wingless on other segmentation genes, suggesting that they function in the wingless signalling pathway. We investigated the roles of these genes by determining their cellular requirements and their effects on wingless protein expression patterns. porcupine is involved in presentation of the wingless signal to its target cells, and dishevelled is required within those cells for reception or interpretation of the signal. In this proposal, we focus on the genetic, molecular and biochemical characterization of dishevelled and porcupine with the ultimate goal of identifying key molecules involved in the int-1 signal transduction pathway.